The invention relates to an improved posterior chamber intra-ocular lens designed for implantation in the eye.
Surgical removal of opaque lenses from the eyes of cataract patients is one of the most common surgical procedures. In the past, contact lenses or spectacles were usually prescribed for the patient to provide at least limited vision following the operation. The optical and other drawbacks of contact lenses and spectacles for such purpose were numerous. Today implantation of an artificial intra-ocular lens to replace the removed opaque natural lens is the preferred way to restore the patients sight.
The natural lens in the eye serves to focus the light entering the eye through the cornea onto the retina. The lens is surrounded by a thin capsule. In cataract surgery either the entire lens, including the capsule, is removed intact in a so called intracapsular extraction or the transparent rear wall of the capsule (the so called posterior capsule) is left in the eye in the so called extracapsular cataract extraction. Extracapsular extraction is now the preferred technique.
The eye is divided by the iris into an anterior chamber in front of the iris and a posterior chamber behind the iris. The implant can be placed either in the anterior chamber or the posterior chamber. Placement in the posterior chamber is now preferred for a number of reasons.
One of the particular advantages of placement in the posterior chamber is that the implant need not be sutured to the eye and can simply be positioned by the use of centering loops or the like extending from the lens body. U.S. Pat. Nos. 4,159,546 and 4,298,994 describe implants of this type designed for implantation in the posterior chamber.
Typically the rear surface of an intra-ocular lens implanted in the posterior chamber contacts the posterior capsule over at least a substantial portion of its surface. This may to some extent impede natural flow of fluids, possibly resulting in some damage to the posterior capsule. The rear surface of the lens can also to some extent abrade the posterior capsule and possibly damage that capsule.
In a small percentage of cases the naturally transparent posterior capsule becomes cloudy following implantation. In this instance the capsule must be opened so that light can be focused onto the retina. Until recently this was normally accomplished by inserting an instrument into the eye to cut through the posterior capsule, i.e., a so called discission. However, this operation is now very easily accomplished on an outpatient basis by the use of a Neodynium YAG laser. The coherent light from the laser is focused directly on the posterior capsule to in effect form a hole in the capsule without any damage to other portions of the eye.
However, if the rear surface of an implant is in contact or closely adjacent the spot on which the laser is focused, that portion of the lens will also be damaged by the laser resulting in a mark on the lens which will appear in the field of vision of the patient.
The patent to Hoffer U.S. Pat. No. 31,626 describes an intra-ocular lens designed for implantation in the posterior chamber and in which an annular lip or ridge is provided on the rear surface of the lens for spacing that surface from the posterior capsule. This is said to facilitate discission by permitting an instrument to be inserted behind the lens and also to discourage or eliminate growth of lens material subsequent to extra capsular extraction.
The present invention relates to an improved intra-ocular lens in which the rear surface of the lens body is provided with a plurality of separated protrusions extending outwardly and rearwardly from the optical portion of the lens to contact the posterior capsule and separate the posterior capsule from the rest of the lens body. This ensures that the optical portion of the lens will not be marked during any operation with a YAG laser. Moreover the protrusions contact only a small area of the posterior capsule minimizing any possible damage to this delicate structure. Fluids can easily circulate between the optical portion of the lens and the posterior capsule and such fluid circulation is not in any way blocked by an annular extended ridge, lip or other structure. In lenses which have an annular lip should the lip after implantation fall into the pupil the distortion will be great. Similarly the lip causes distortion in the field of view of a surgeon who has to repair retinal detachment subsequent to implantation. The use of protrusions avoids both these difficulties. As in other lenses of this type, appendages, for example haptic loops or the like, extend from the lens body for positioning the lens within the eye after implantation.
In a first embodiment of the present invention the protrusions are an integral part of the lens body and are disposed about a central optical portion. The appendages which position the lens body are also an integral portion of the lens body.
In a second embodiment of the present invention the protrusions are fixed to the lens body in bore holes which are drilled in the rear surface during manufacture. Conventionally, one or two such bore holes are provided through the lens for facilitating insertion during the surgical procedures so drilling additional holes does not substantially complicate manufacture.
Utilizing protrusions which are separate from the lens body permits the protrusions to be of a different material which may be more friendly to the eye. It may be desirable to utilize material such as silcone or hydroxy ethyl methacrylate (HEMA) commonly known as "soft lens" material which is softer than the polymethylmethacrylate now conventionally used as the material for the lens body. Both materials are compatible with eye tissue.
In addition, utilizing separate protrusions enables the surgeon or the manufacturer to very readily adapt any given lens to select any desired material, size of protrusion or number of protrusions. The protrusions may be in the form of a ring which is anchored at one or more locations to a bore hole with separated protrusions extending outwardly therefrom.
Other objects and purposes of the invention will be clear from the following detailed description of the drawings.